This invention relates to a process for the preparation of a vanadyl/vanadous sulphate crystal product or solution from a vanadium bearing ore material, and to various intermediate steps in the process.
Vanadyl/vanadous sulphate solutions or electrolytes are becoming more and more important in various applications, including in the battery industry. A problem with the solutions, however, is that they are highly acidic and hazardous. Accordingly, there may be serious problems in transporting these products around the world.
Additionally, there are many vanadium bearing ores that would be useful as a starting material for producing vanadyl/vanadous sulphate solutions. However, as far as we know, there is to date no commercially viable process for producing vanadyl/vanadous sulphate solutions from vanadium bearing one.
According to a first aspect of the invention, a process for the preparation of vanadyl/vanadous sulphate crystals from a vanadyl/vanadous sulphate solution, and subsequent reconstitution of the crystals to form a solution, comprises the step of:
1) providing a starting material in the form of a vanadyl/vanadous sulphate solution having a specified chemical composition.
2) evaporating the solution to crystallization by applying heat; and
3) re-dissolving the crystals by the addition of a specified volume of de-ionized water with constant stirring and, if necessary, with the addition of heat to form a clear solution having substantially the same chemical composition as the starting material.
The necessity of applying heat in step 3) is dependent on the evaporation in step 2). If the vanadyl/vanadous sulphate solution is evaporated at its boiling point, the water of crystallization is removed from the crystals and heat is required for dissolution of the crystals in step 3). If however, the vanadyl/vanadous sulphate solution is evaporated at below its boiling point, for instance below 90xc2x0 C., the water of crystallization is not removed from the crystal structure and no heat is required for dissolution of the crystals in step 3).
The invention encompasses a process for the preparation of a vanadyl/vanadous sulphate solution from vanadyl/vanadous sulphate crystals by dissolving the crystals in a specified volume of de-ionized water with constant stirring, and, if necessary, with the addition of heat.
The vanadyl/vanadous sulphate solution is prepared by forming a vanadous sulphate solution from a vanadyl sulphate solution electrolyzed with sulphuric acid, and combining the vanadous sulphate solution with a further portion of vanadyl sulphate solution, preferably in equal volumes and/or concentrations, and if desired filtering the resultant solution and adding phosphoric acid as required.
The vanadyl sulphate solution is preferably formed by reacting sulphuric acid, diluted with de-ionized water as required, with vanadium pentoxide and oxalic acid under suitable reaction conditions.
The sulphuric acid solution preferably has a molarity of about 2.8 to about 8.5 depending upon the specified molar concentration of the vanadyl sulphate solution.
The oxalic acid is preferably pure oxalic acid, in particular 99% pure or greater.
The vanadium pentoxide is also preferably pure, in particular having a V2O5 content of 99.5% or greater.
The vanadyl sulphate solution produced may have any desired molar concentration, for example 2M, 4M up to a maximum of 6M.
The pure V2O5 is preferably produced by forming a slurry containing ammonium-poly-vanadate (APV), contacting the slurry with ammonia gas to precipitate out ammonium-meta-vanadate (AMV), and calcining the AMV in a kiln to form pure V2O5.
Ammonium sulphate is preferably added to assist in precipitating the AMV from the APV slurry.
The ammonia gas is preferably added to the slurry very slowly to completely dissolve the APV before crystallization of the AMV.
The APV is preferably produced from a titaniferous magnetite ore.
According to a further aspect of the invention, there is provided a process for producing a vanadyl/vanadous sulphate crystal product or solution from a vanadium bearing ore material, in particular a titaniferous magnetite ore starting material incorporating, as appropriate, one or more of the above method steps.
The invention also extends to the use of a vanadyl/vanadous sulphate solution produced according to any one or more of the above method steps or reconstituted from a vanadyl/vanadous sulphate crystal product produced according to any one or more of the above method steps as an electrolyte in a vanadium redox battery.